WASHINGTON -- U.S. President Donald Trump says that Energy Secretary Rick Perry -- a key player in the controversy over Trump's dealings with Ukraine -- will leave his position by the end of the year.

In making the announcement on October 17, Trump said that he would nominate a successor soon. He said he already had identified the person he would name.

'We already have his replacement. Rick has done a fantastic job. But it was time,' Trump said.

The announcement confirmed recent press reports that Perry would be stepping down in the near future.

An official said Perry was with the president earlier in the day when he shared the news aboard Air Force One on the way to Perry's home state of Texas for a campaign rally.

The U.S. administration has gone through a high level of turnover of top officials and cabinet members during Trump's presidency, which began in January 2017.

Democrats in the U.S. House of Representatives have issued a subpoena to Perry as part of an impeachment inquiry into dealings with Ukraine.

The subpoena asks to Perry to provide documents related to a Ukrainian state-owned oil and gas conglomerate, Naftogaz, as well as his involvement in a July 25 call between Trump and Ukrainian President Volodymyr Zelenskiy.

Trump has said Perry encouraged him to make the July 25 call, in which the U.S. president pressed Ukraine to investigate his Democratic rival Joe Biden and his son, who was on the board of a Ukrainian gas company

Perry, a former governor of Texas, who faced Trump in the 2016 Republican primary elections, has previously denied published reports that he was planning to resign in November.